The present invention relates to devices for oxygenating oxygen enrichable fluid, e.g. blood, and in particular to gas-permeable, liquid-impermeable membrane oxygenators having a gas pressure relief valve.
During cardiovascular surgery, oxygenators and other types of devices are utilized to carry out the function of the patient's heart and lungs. While various types of oxygenators are known, the basic two types of oxygenators are the bubble oxygenators and the gas-permeable, liquid-impermeable membrane oxygenators. Bubble oxygenators function by bubbling an oxygen bearing gas into the blood. Membrane oxygenators perform the transfer of oxygen and carbon dioxide between the blood and an oxygen rich gas across a gas-permeable, liquid-impermeable membrane.
In particular, membrane oxygenators include a gas-permeable, liquid-impermeable membrane mounted in a housing to define separate blood and gas flow pathways. The membrane selectively allows passage of molecular oxygen and carbon dioxide, while preventing the transfer of fluid, i.e. water. The transfer of the oxygen and carbon dioxide across the membrane occurs because of the concentration difference between these gases in the oxygen-depleted blood and oxygen rich gas, which transfer is known as diffusion.
While it is desirous to effect the transfer of oxygen and carbon dioxide, the pressure of the oxygen enriched gas must be maintained low enough to inhibit the forcing of large quantities of the gas through the membrane. Such an increase may occur if the gas outlet port becomes occluded for any reason. When the gas side pressure exceeds the blood side pressure, gross size bubbles of the gas will be forced into the blood side fluid pathway. These bubbles present the danger of stroke or even death to the patient when they pass from the oxygenator into the patient's blood stream.
One particular known membrane oxygenator employs a plurality of hollow microporous fibers as the gas-permeable, liquid-impermeable membrane. These hollow fibers are arranged in a bundle mounted in the housing. The fibers are arranged to position the respective opposite open end of each fiber at either end of the housing. Each respective housing end is formed with a cavity isolated from the main internal housing cavity. Thus a fluid flow pathway is formed by the combination of these cavities and the interior of the multiple fibers. The blood or oxygen rich gas is passed through this defined flow pathway, while the other is passed through the main housing cavity, which defines a separate fluid flow pathway.
The release of excess gas to reduce the pressure in the gas flow pathway has heretofore not been performed with membrane oxygenators using pressure relief valves. Typical procedures for maintaining the gas pressure within an exceptable range involves a careful monitoring and control of the gas pressure. Furthermore, oxygenators have been designed which merely vent excess gas to the atmosphere. These types of oxygenators isolate the blood from the atmosphere by passing the blood through the hollow fibers forming the gas-permeable, liquid-impermeable membrane.
The main disadvantage with oxygenators having such vents pertains to a procedure used to prime the oxygenator prior to introduction of the blood. Generally, such procedure involves flushing the interior of the oxygenator with carbon dioxide gas. The carbon dioxide gas removes any gas in the oxygenator prior to the introduction of the blood. The major disadvantage with such vented oxygenators is that the carbon dioxide gas escapes during the flushing procedure, and does not provide any beneficial flushing of the oxygenator.
It can thus be seen that it would be highly desirable to provide an oxygenator which has a means for regulating the gas pressure without the above described disadvantages.